Composite structures, in particular, carbon fiber/resin materials, are rapidly increasing in use, and are of particular interest to the aerospace industry where there is a need for high strength-to-weight structures. A similar need exists in the watercraft and automobile industry where high-strength/light-weight bodies and other structural parts are being used for possible weight reduction for increased fuel efficiency.
One favorable characteristic of carbon-resin composites is that the composite exhibits physical characteristics particular to the matrix resin. For example, if the resin has properties of high thermal resistivity or being fire retardant, then the composite made from that matrix resin will, to some extent, exhibit those properties as well. Thus, the particular resin chosen for each application is typically not chosen just for its structural properties, but also for whatever other desired characteristics might be best suited for the application.
Though composite structures typically exhibit improved structural properties in comparison to the resin itself, there are still many limitations in the formation of composite structures. One such limitation in composites is the physical bond that exists between the resin and the carbon fibers of the composite. In order for the composite to have any load-carrying capability, it is necessary for the resin to be in close proximity (usually mechanically locked) to the fiber. Thus, carbon-resin composite technology depends on the formation of a strong bond between a fiber substrate and a resin matrix; and the bond interaction parameters are analogous to those found in adhesive bonding processes.
The chemical bond between resin and fiber material, i.e. at the interface between the fiber and the matrix resin, is typically a limiting factor in the strength of a composite material. The “interface” is usually one molecular layer thick, i.e., nanolayer, and refers to the meeting of the resin material with the surface of the fiber; and all these are governed by the interactions that occur in the nano (monomolecular) layer of the resin/fiber interface. In contrast, the “interphase” is of macroscopic dimensions and describes macroscopic qualities of the composite. It is the combination of the interface and interphase properties of the material that determines the behavior of a composite. Thus, it is the surface area and roughness of the reinforcement (fiber), the wetting properties of the matrix, and the differences in thermal and mechanical properties of the constituents that are strongly involved in determining the interaction, bonding and strength of a composite.
It is desired to produce a composite of improved strength where the resin material is intimately bonded to the surface of the composite fibers, thus forming strong interfacial bonds within the composite. It is further desired to produce a composite material having improved strength and interfacial bonding from a resin having desirable physical and chemical characteristic such that the resultant composite exhibits the physical/chemical characteristics of the resin.